1. Field of the Invention
The present invention relates to a vehicular power transmission apparatus and, more particularly, to a vehicular power transmission apparatus enabled to perform an idle stop.
2. Description of Related Art
In recent years, an idling stop vehicle configured to stop fuel supply to an engine at vehicle stop or the like to thereby stop an idling operation of an engine, and a hybrid vehicle configured to arbitrarily switch between an engine drive mode and a motor drive mode during running have become widespread. There are requests for maintaining accessories, such as an air conditioner compressor and a water pump, which operate interlockingly with rotations of a crankshaft of an engine of each of the idling stop vehicle and the hybrid vehicle, in operating states even when the engine is stopped.
Thus, hitherto, there has been proposed a vehicular power transmission apparatus configured such that when accessories are driven while an engine is stopped, the crankshaft of the engine is separated from a transmission member for transmitting rotations among the crankshaft of the engine, the rotating shaft of a motor generator, and the rotating shafts of accessories (see, e.g., Japanese Patent Unexamined Publication No. JP-A-11-147424).
As illustrated in FIG. 25, a vehicular power transmission apparatus disclosed in JP-A-11-147424 has an engine 1, a transmission 2, and a motor generator 3 functioning as both of a motor and a generator. The crankshaft of the engine 1 and the rotating shaft of the motor generator 3 are connected to each other via a belt 10 and pulleys 11 and 12. Further, the motor generator 3 is connected to a battery 6 via an inverter 7. The inverter 7 adjusts electric power supplied from the battery 6 to the motor generator 3 and drives the motor generator 3 such that the number of revolutions of the motor generator 3 is variable.
The vehicular power transmission apparatus of the above configuration drives the motor generator 3 to start the engine 1 and causes the motor generator 3 to function as a generator after the engine 1 is started. The inverter 7 charges electric power generated by the motor generator 3 to the battery 6. Incidentally, an operation of the inverter 7 is controlled by a controller 9.
The rotating shafts of an air conditioner compressor 4 and a power steering oil pump 5 are connected to the crankshaft of the engine 1 and the rotating shaft of the motor generator 3 via the belt 10 and the pulleys 13 and 14. The compressor 4 and the oil pump 5 are driven by the engine 1 when the engine 1 is operated. However, the compressor 4 and the oil pump 5 are driven by the motor generator 3 when the engine 1 is stopped.
Further, an electromagnetic clutch 8 is interposed between the crankshaft of the engine I and the pulley 11. The engagement or disengagement of the electromagnetic clutch 8 is controlled by a controller 9. When the compressor 4 and the oil pump 5 are driven by the motor generator 3 while the engine 1 is stopped, the electromagnetic clutch 8 is disengaged, so that the crankshaft of the engine 1 is separated from the belt 10.
A clutch for disengaging the crankshaft of the engine from the transmission member which transmits rotations among the crankshaft of the engine, the rotating shaft of the motor generator and the rotating shaft of the accessories in the vehicular power transmission apparatus disclosed in the JP-A-11-147424 is required to meet at least the following operating conditions (1) to (4).
(1) When the engine is started by the motor generator, the clutch engages the crankshaft of the engine with the above transmission member.
(2) When the motor generator and the accessories are driven by the engine while the engine is operated, the clutch engages the crankshaft of the engine with the above transmission member.
(3) When the engine is stopped, the clutch engages the crankshaft of the engine with the above transmission member.
(4) When the accessories are driven by the motor generator while the engine is stopped, the clutch disengages the crankshaft of the engine from the above transmission member.
Incidentally, the operating condition (3) is set for stopping the engine using the motor generator and the accessories as a load in order to instantly stop the engine and to enable the vehicle to pass the resonance point thereof quickly when the engine is stopped.
According to the operating conditions (1) to (3), a drive element and a driven element selected from the engine and the motor generator are arbitrarily interchanged therebetween. Thus, the clutch is required to be able to connect therebetween regardless of whichever of the engine and the motor generator is the drive element. Further, according to the operating condition (4), the clutch is required to be able to disengage the engine and the motor generator at least in a rotational direction in which the motor generator is the drive element.
An electromagnetic clutch has relatively high degree of design freedom regarding the setting of engagement or disengagement. Thus, the electromagnetic clutch relatively easily meets the operating conditions (1) to (4). However, the electromagnetic clutch needs a controller for controlling thereof, and an electric actuator. In a case where the electromagnetic clutch includes such a controller and the electric actuator, the size of the electromagnetic clutch is increased. In addition, the cost thereof is increased. More specifically, the limitation of space of an engine room is high. Thus, a clutch of a large size is disadvantageous in mounting thereof in the engine room.